Field of the Invention
The embodiments of the present invention relate to an organic light emitting device, and more particularly, to an organic light emitting device, which may be driven at a low voltage and has improved luminescence lifetime, and a method of fabricating the same.
Discussion of the Related Art
An organic light emitting display (OLED) is a self light emitting display device, and is a display device based on an organic light emitting device that injects electrons and holes from each of a cathode for electron injection and an anode for hole injection into a light emitting layer and emits light when excitons obtained by combination of the injected electrons and holes are transited from an excited state to a ground state.
The organic light emitting display may be categorized into a top emission type, a bottom emission type, and a dual emission type depending on a direction to which light is emitted, and may be categorized into a passive matrix type and an active matrix type depending on a driving mode.
The organic light emitting display may be fabricated at a lightweight and slim size as it does not need a separate light source unlike a liquid crystal display (LCD). Also, the organic light emitting display is favorable in view of power consumption due to low driving voltage and also is excellent for color realization, response speed, viewing angle, and contrast ratio (CR), whereby the organic light emitting display has been studied as a next generation display.
As a display of high resolution has been developed, the number of pixels per unit area has been increased and high luminance has been required. However, there is a limitation in luminance Cd of a unit area A in view of a luminescent structure of the organic light emitting display, and a problem occurs in that reliability of the organic light emitting device is deteriorated and power consumption is increased due to increase of an applied current.
Therefore, to overcome a technical limitation which is a factor that deteriorates quality and productivity of the organic light emitting device, it is required to improve luminescence efficiency and lifetime of the organic light emitting device and reduce power consumption. In this respect, various studies for developing an organic light emitting device, which may improve luminescence efficiency, lifetime of an organic light emitting layer and viewing angle characteristic while maintaining a color area, have been made.
An organic light emitting device (OLED) generally emits light through recombination of holes and electrons in an organic light-emission layer (EML), wherein the holes are injected from a first electrode (anode) and moved through a hole injection layer (HIL) and a hole transporting layer (HTL) and the electrons are injected from a second electrode (cathode) and moved through an electron injection layer (EIL) and an electron transporting layer (ETL).
In the organic light emitting device, to increase luminescence efficiency of the organic light emitting layer, the holes and the electrons should be injected at high density.
Also, since the organic light emitting device emits light strongly through recombination occurring at a point where the holes meet the electrons in an organic light emitting layer, not emitting light in a full area of the organic light emitting layer, its characteristic may be improved in such a manner that the recombination area is reflected in design of the organic light emitting device.
Generally, in configuring red, green and blue sub pixels in a top emission type organic light emitting device, a luminance ratio of the green sub pixels is the highest, whereby it is important to increase luminescence efficiency of a green emission layer in the organic light emitting device. As a result, studies for applying a green phosphor host material having high luminescence efficiency in comparison with the existing green fluorescent host material to the green emission layer have been made.
Also, a general method of fabricating an organic light emitting device may include a thermal evaporation method that forms a functional layer and an organic light emitting layer, which are required in the organic light emitting device, by selectively forming an organic material layer using a fine metal mask.
In the organic light emitting device fabricated by the aforementioned fine metal mask type, the organic light emitting device that includes a green emission layer to which a green phosphor host material is applied has an advantage of high luminescence efficiency but has a problem in deterioration of lifetime in comparison with the organic light emitting device that includes a green emission layer to which the existing green fluorescent host material is applied. Therefore, it is required to improve the lifetime of the organic light emitting device.
Also, in the organic light emitting device that includes a green phosphor host material, it is required to reduce power consumption through efficiency improvement and driving voltage reduction.